This invention relates to a method and apparatus for producing packets containing a flowable material, in particular but not necessarily exclusively an infusible material such as tea or coffee, equipped with means for applying pressure to express liquid from the packets after infusion, and to packets having such means.
It is well known that when using infusion packets such as tea or coffee bags, a significant part of the infusion remains in the bag unless it is wrung or squeezed out. Many proposals have been made to allow this to be done without having to touch the bag itself, by providing threads or draw-strings that can be pulled to contract the bag. In the examples of U.S. Pat. Nos. 3,539,355, 3,237,550, 2,881,910, 2,878,927 and 2,466,281 the draw-string is threaded through holes in the bag walls but that has the immediate disadvantage that the infusible material can easily leak out before use. In addition, the holes weaken the bag walls and, especially when the bag has been wetted, bring the risk of tearing the bag as the threads are pulled, and releasing more of the solid infusible material.
WO91/13580 shows analogous examples in which the thread may be retained at desired locations by staples driven through the bag walls, which similarly create leakage paths and local weaknesses at regions where the thread tension is likely to be applied to the bag.
Other proposals are disclosed in U.S. Pat. No. 3,415,656, and WO92/06903 which show bags which have their main envelope formed by two rectangular layers of sheet material heat-sealed together around their edges. A loop of thread is held in the bag by being trapped in the heat sealed margins at least at one region of those margins remote from one end of the bag where the ends of the loop emerge through the heat sealed margin at that end. This arrangement introduces another potential problem in that the heat seal where the thread is trapped is placed under stress when the bag is contracted and if it fails the bag is opened. Since this is likely to occur at the lower end of the bag, the solid contents would be spilled immediately. It may also be noted that these earlier proposals do not suggest how the infusion packets they describe can be economically produced.